Beam pumping units or pump jacks are known for driving reciprocating pumps located downhole in the bore of a subterranean oil well. A string of sucker rods is suspended from the carrier bar of the pump jack. A polish rod at the top of the string of sucker rods connects to the carrier bar and extends downwardly through a stuffing box seal at a wellhead. The polish rod connects to the string of sucker rods extending downhole to the pump.
In operation, the reciprocating rods tend to rub against the inside of the production tubing, causing wear to the rods, rod couplings, and tubing. This occurs particularly in the cases of slanted wells where the rods tend to rest on the lower side of tubing. To limit or distribute the inevitable wear, a rod-rotator is used to incrementally rotate the polish rod each pump stroke.
The polish rod is suspended by a polish rod clamp atop the carrier bar or rod-rotator. The carrier bar is suspended from the horsehead of the pump jack by a cable bridle. The polish rod extends through the carrier bar. Misalignment of the polish rod and the carrier bar can result in contact of the carrier bar and polish rod. A rod-rotator is in turn supported by the carrier bar. Subsequent rotation of the polish rod results in circumferential scoring a the interface of the carrier bar and the polish rod.
Examples of misalignment between the carrier bar and the polish rod include:
mechanical misalignment of the carrier bar; PA1 a slow or restricted downstroke and a resultant slackening of the cable bridle causing angular movement of the carrier bar; and PA1 a misaligned polish rod extending from the wellhead seal. PA1 providing a cylindrical sleeve having a bore therethrough and an upset at one end; PA1 installing the sleeve into the top of the bore extending through the carrier structure, retained therein by the sleeves upset; PA1 installing the polish rod through the bore of the sleeve; and PA1 suspending the polish rod from the top of the carrier structure so that the sleeve guides the polish rod through the carrier structure without contact of the polish rod and the carrier structure and thereby preventing circumferential scoring of the polish rod when the rod is rotated by the rod-rotator.
The polish rod is expected to carry high cyclical loading so as to support rod string loads on the upstroke of about 13,000-40,000 pounds. If a polish rod were to fail at a stress riser, such as at a circumferential score, the rod string could fall into the well, potentially releasing well fluid (oil or gases) from the stuffing box seal and initiating an expensive recovery operation.
Preventative maintenance regularly calls for replacement of scored polish rods before they fail. Replacement polish rods can cost $700 to $1200 each. As stated above, polish rod failure can result in the escape of oil and gas and force an expensive cleanup and rod recovery process.
An example of a rod-rotator is the Hercules (registered trademark) Rod Rotator available from Flow Control Equipment, Borger, Tex. The Hercules Rod Rotator sits atop a leveling plate which in turn sits atop the carrier bar. Hercules specifies an aluminum pilot bushing which fits between the leveling plate and the rotator. The bushing comprises a ring with a short depending portion to mate with and center the bushing in the leveling plate. The polish rod extends therethrough and is centered relative to the rod-rotator and the leveling plate. The prior art bushing does not fix the relationship between the polish rod and carrier bar.
The polish rod is still subject to misalignment and wear as it extends from the bottom of a misaligned carrier bar.
Accordingly, there is a need for a way to protect a rotating polish rod from circumferential scoring regardless of the positioning or style of the rod-rotator.